Which of the following fluids can be classified as non–newtonian?
Try it first: pick an option, then read the explanation.
Correct answer: B. Human blood and Toothpaste
Asked in SSC JE 2 MARCH 2017 Morning Shift
Detailed Explanation
Fluids that deviate from Newton's linear viscosity relation are non-Newtonian. These fluids exhibit shear-dependent viscosities or require a threshold yield stress.
Why “Human blood and Toothpaste” Is Correct
Human blood is a shear-thinning (pseudoplastic) suspension, and toothpaste is a Bingham plastic requiring an initial yield stress before flowing. Both are non-Newtonian.
| Fluid type | Viscosity changes with rate of shear? | Examples |
|---|---|---|
| Ideal fluid | No (μ = 0) | Theoretical only |
| Newtonian fluid | No (μ = const) | Water, air, oil, mercury |
| Non-Newtonian | Yes | Blood, toothpaste, ketchup, paint |
| Ideal plastic (Bingham) | No, but needs yield stress τ₀ first | Fresh concrete, drilling mud |
Why the Other Options Are Wrong
- A. Kerosene oil and Diesel Oil: Kerosene oil and diesel oil are Newtonian fluids.
- C. Diesel oil and Water: Diesel oil and water are both Newtonian fluids.
- D. Kerosene oil and Water: Kerosene oil and water are both Newtonian fluids.
Key Point
Human blood and toothpaste are non-Newtonian fluids.
Key Concepts for Students
- Blood viscosity decreases as shear rate increases (shear thinning).
- Toothpaste will not flow out of a tube without applied pressure exceeding its yield stress.
- Water, kerosene, diesel, and air are classical Newtonian fluids.
Practice more: this is question 69 in Properties of Fluid MCQs – Part 5. Try the whole set and check every answer instantly.